Deep vein thrombosis (DVT) or pulmonary embolus affect 1-3 per 1000 yearly of the adult population, or nearly 200,000 per year, with an incidence that rises exponentially with age. The burden of venous thrombosis predominantly involves DVT, which is complicated by post-thrombotic syndrome (PTS) in 20- 50% of cases. PTS has a spectrum from mild edema to disabling symptomatic disease with trophic skin changes, chronic pain, and venous skin ulceration. While PTS is thought to occur as a result of damage to the venous valves with resultant reflux or chronic venous obstruction limiting outflow, additional etiologic determinants of PTS have not been extensively studied. We propose a population-based study to evaluate the molecular determinants of chronic peripheral venous disease (CPVD) in a multi-ethnic general population sample, the San Diego Population Study (SDPS). Participants had detailed physical examination and duplex leg ultrasound to establish presence of CPVD based on anatomic and clinical findings. We will address the following hypotheses: 1. Among those with hereditary disorders associated with the hypercoagulable state ("hereditary thrombophilia") there will be an increased risk of deep functional venous disease (DFD) assessed by duplex ultrasound and of superficial venous functional disease (SFD) when it occurs in the absence of DFD and together with clinical features of PTS. 2. There will be an increased risk of DFD or SFD with features of PTS, among participants with higher levels of biomarkers reflecting different aspects inflammation. 3. Given the association of obesity with the risk of CPVD and PTS, there will be an increased risk of DFD or SFD with features of PTS in association with higher levels of biomarkers reflecting adipocyte products. To test these hypotheses phenotypic and genetic molecular biomarkers will be measured in stored biological specimens of the SDPS participants including 370 control participants and 370 cases of CPVD, focusing on post-thrombotic syndrome. Findings will allow hypotheses to be formed concerning etiologic factors in the development of PTS after clinically diagnosed or clinically silent DVT. PTS and CPVD affect 2.5 million people in the United States; 20% develop severe disease with venous ulcers. Resultant disability is estimated at 2 million lost workdays/year and medical costs as $300 million yearly. Findings here can form the basis for development of new therapies to treat, and moreover prevent, PTS.